The origin of an unusual sex chromosome constitution in Acomys sp. (Rodentia, Muridae) from Tanzania
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This paper describes a case which presents an evident variation from the “standard” XX/XY sex chromosomal constitution in a rodent, Acomys sp. This species known to be found in three localities of East Africa has only recently been separated from A. spinosissimus, its closest relative. In our study, five specimens of Acomys sp. and eight specimens of A. spinosissimus were live-trapped in five localities. Comparisons between the two taxa assed by G- banding show a complete homology in the chromosomal shape and banding pattern for 29 pairs of chromosomes corresponding to the complete autosomal set of A. spinosissimus. However, while all the A. spinosissimus analysed have 2n = 60 and a XY-XX system, in Acomys sp. males and females constitute mosaics for sex chromosomes in the bone marrow cells. Females (2n = 59, 60) have an excess (97%) of aneuploid cells with one single giant X chromosome, and males (2n = 60, 61) show X0/XY cells occurring in somatic tissues and XY cells in the germinal lineage. In addition, an odd heterochromatic submetacentric chromosome was identified in all the cells examined in two males and a female of Acomys sp. Since this chromosome was not related to sex determination and it is not present in all the analysed specimens, it can be considered as a B chromosome. Finally, the in situ fluorescence hybridisation (FISH) with telomeric probes showed a very intense interstitial telomeric signal (ITS) at the medial part on the long heterochromatic arm of the X chromosome. This could be due to recent chromosomal rearrangement.
KeywordsAcomys spinosissimus African rodent B chromosome Cytotaxonomy Mosaicism Sex chromosome Telomeric sequences In situ fluorescence hybridisation
This work has been supported by a European Union, 5th framework RTD Program “Staplerat”, Progetti d’Ateneo (MC). We thanks Ernesto Capanna for helpful suggestion on an early version of the manuscript.
- Close RL (1984) Rates of sex chromosome loss during development in different tissues of the bandicoots Perameles nasuta and Isoodon obesulus (Marsupialia: Peramelidae). Austr J Biol Sci 37:53–61Google Scholar
- Evans EP, Breckon G, Ford CE (1964) An air-drying method for meiotic preparations from mammalian testes. Cytogenetics 3:289–294Google Scholar
- Fredga K (1994) Bizarre mammalian sex-determining mechanisms. In: Short RV, Balaban E (eds) The differences between the sexes. Cambridge University Press, Cambridge, pp 397–418Google Scholar
- Jones RN, Rees H (1982) B chromosomes. Academic Press, New YorkGoogle Scholar
- Hayman DL, Martin PG (1974) Mammalia 1: Monotremata and Marsupialia. In: John B (ed) Animal cytogenetics 4. chordata. Gebrüder Borntraeger, Berlin, 110 ppGoogle Scholar
- Hsu TC, Patton JL (1969) Bone marrow preparations for chromosome studies. In: Benirschke K (ed) Comparative mammalian cytogenetics. Springer-Verlag, pp 454–460Google Scholar
- Musser GG, Carleton MD (2005) Superfamily Muroidea. In Wilson DE, Reeder DM (eds) Mammal species of the world a taxonomic and geographic reference. Johns Hopkins University Press, Baltimore, pp 894–1531Google Scholar
- Ohno S, Jainchill J, Stenius C (1963) The creeping vole (Microtus oregoni) as a gonosomic mosaic. I. The 0Y/XY constitution of the male. Cytogenetics 2:232–239Google Scholar
- Ohno S, Stenius CH, Christian I (1966) The X0 as the normal female of the creeping vole (Microtus oregoni). In Darlington CD, Lewis RK (eds). Chromosomes today, vol 1. Oliver and Boyd, Edinburgh, pp 182–187Google Scholar